The optical volume scattering function (VSF) defines the angular distribution of scattered light
within an element of water. The VSF is dominated by scattering from particles, and strongly depends
on concentration, particle size, and composition. Despite the importance of the VSF, it has seldom
been measured in the field. Here we report some of the first field VSF measurements in decades, made
in the nearshore bottom nepheloid layer (BNL) off the coast of Martha's Vineyard, Massachusetts.
Specifically, we continuously measured the near-forward VSF for several weeks with two co-located
laser scattering instruments (LISST-B and LISST-floc, Sequoia Scientific), covering an angular range
of roughly 0.01 to 15 degrees, an order of magnitude further near-forward than the venerable
observations of Petzold decades ago.

An understanding of near-forward VSF variability in the BNL is needed: for assessment of diver
visibility; for effective marine operations such as underwater navigation, object detection, and
imaging; and for modeling the light field for shallow water remote sensing studies. Dependence on
size proves particularly thorny for prediction of optical properties since size distribution in the
BNL is strongly mediated by bottom stress and turbulence. However, given appropriate models, the
dependence of the VSF on particle size allows us to describe particle dynamics with high temporal
resolution using optical sensors.

In the field, we observed marked variability in the shape and magnitude of the near-forward
VSF over the course of resuspension and settling events. Furthermore, we observed correlation between
total scattering and VSF shape which are explained well by conceptual models of particle dynamics.
In this study, we compare the measured VSF with theoretical optical models, such as Mie theory
and Fraunhofer diffraction, as well as examine the link between VSF shape and magnitude as a
first attempt to constrain and model scattering in the BNL.